1. Technical Field
The invention relates to the field of gas generators, and more particularly to a pressure swing adsorption apparatus.
2. Background Art
On Board Inert Gas Generating Systems (OBIGGS), or On Board Oxygen Generating Systems (OBOGS) utilize molecular sieve by employing a pressure swing adsorption (PSA) process that have been used for many years to generate either Nitrogen or Oxygen product gas respectively. This known PSA technology uses compressed air or conditioned engine bleed air fed through a valve or valves to pressurize molecular sieve contained in one of a number of canisters. After a predetermined period of time, the valve changes state, venting the one canister full of sieve, then pressurizing the next canister. This process of pressurization and venting is the PSA process. Previous PSA systems have been controlled by a rotary valve, driven by a fixed or variable speed motor. Still others utilize a system of dedicated independent valves to control each pressurization and each venting cycle for each canister or bed.
Known PSA systems have utilized a linear 4-way slide valve, which connects input air port with the first canister, while connecting a vent port with the second canister. The valve changes state, which connects the vent port with the first canister and simultaneously connecting the second canister with the input air. The linear 4-way slide valve simplifies the complex system of independent dedicated valves necessary on some systems. The linear valve has also proven to be more reliable then either the rotary valve or the system of valves, accomplishing the same tasks.
The linear valve used on typical PSA systems is pneumatically operated. Miniature pilot solenoid valves that are opened and closed using solid state electronics, housed in an EMI shielded enclosure control pilot gas. The pilot solenoids provide gas pressure to two gas cylinders, which are connected to a sliding block. The block slides across a mating plate with three openings or ports. The ports are constructed in a straight line. The outer ports are equal-distance from center port. The sliding block has an undercut, which acts as a flow path. The flow path is sized to connect two of the three ports at any one point in time. A controller is set to open and close the miniature pilot valves at a predetermined time.
The use of a system of valves in a sequencing scheme to conserve compressed air has been explored in a shipboard nitrogen system. By using venting gas to start the pressurization of the sequential canister, new air could be saved. This “reusing” of compressed air in a finite air source PSA system demonstrated that the overall efficiency of the system could be improved, providing a series of options for reducing compressor size, reducing system size, or providing higher product output.
In some applications, the source of new air is limited. Many airborne and ground based systems have a finite source of air. There are many uses for bleed air on rotary and fixed wing aircraft, hence conserving the available air is critical. There have been a number of studies conducted for various concepts for air conservation. A number of these studies have resulted in patents, such as U.S. Pat. Nos. 5,858,063, 6,409,807, and 5,074893.
The drawback to known systems is that they generally depend on high number of independent two-way and three-way solenoid valves to perform the air conservation process or principles. The present invention utilizes a highly reliable slide valve device, which normally operates like a four-way valve. In the present invention, the device provides a new communication path for airflow, which produces the desired air reuse, or conservation, without the unnecessary complication of numerous valves. The reduction of parts and improving air use results in a reduction in weight which is critical to airborne applications of either oxygen or nitrogen systems.
While the above cited references introduce and disclose a number of noteworthy advances and technological improvements within the art, none completely fulfills the specific objectives achieved by this invention.